Hydraulic accumulator, in particular a membrane accumulator

ABSTRACT

The invention relates to a hydraulic accumulator, preferably a membrane accumulator, in particular for damping pulsations in fluid circuits, comprising an accumulator housing ( 12 ), with at least one inlet ( 14 ) and an outlet ( 16 ) for the fluid for damping, whereby a separating element ( 18 ), preferably in the form of a membrane, separates a gas reservoir ( 20 ) from a fluid chamber ( 22 ) within the accumulator housing ( 12 ). According to the invention, a hydraulic accumulator with high working capacity of high reliability which little space requirement despite high accumulation capacity for the working gas in the gas reservoir ( 20 ) can be achieved, whereby an embodiment has a support device ( 24 ) within the accumulator housing ( 12 ), running within the gas reservoir ( 20 ) or defining the same, forming a possible support for the separating element ( 18 ) and the gas reservoir ( 20 ) of the accumulator housing ( 12 ) is sufficiently large in dimension that the total necessary gas volume is retained within the accumulator housing ( 12 ) itself and/or alternatively the membrane is formed from an elastic material, in particular a rubber material and comprises polytetrafluoroethylene or compounds thereof as a gas barrier layer.

The invention relates to a hydraulic accumulator, in particular a membrane accumulator, specifically for damping pulsations in fluid circuits, having an accumulator housing with at least one inlet and an outlet for the fluid to be damped, a separating element, preferably in the form of a membrane, separating a gas supply chamber from a fluid chamber inside the accumulator housing.

Depending on the mode of operation hydraulic accumulators are based on the principle of bubble and membrane accumulators or liquid sound dampers. In hydropneumatic dampers the compressibility of a gas (mostly nitrogen) is used for damping. In the case of a bladder accumulator, for example, the bladder is compressed or expanded as a function of the magnitude of the variations in pressure. A similar behavior is exhibited by membrane accumulators as well. Specifically hydropneumatic dampers (pulse-tone pulsation dampers) were developed because damping may be impaired because of disadvantageous connection of the hydraulic fluid to the volume of gas when standard bladder or membrane accumulators are used. Dampers of this type have an in-line connecting block by means of which the variations in volume or pressure are optimally coupled to the gas volume. Good damping properties up to a frequency of around 500 Hz can be obtained with these dampers (see Mannesmann-Rexroth design projects “Konstruktion von Hydroanlagen” (Construction of Hydraulic Facilities), Der Hydrauliktrainer, Vol. 3, 1st Edition, page 106).

In the known solutions in the state of the art such as are readily available commercially, a connecting point is provided in the accumulator housing to increase the gas supply volume by mounting on the gas supply side an accumulator cylinder in which the additional operating gas, in particular in the form of nitrogen, is stored. The respective known solutions are costly in manufacture, and in addition are geometrically large and sealing problems may arise at the connecting point in question and thus lead to loss of operating gas. In order to improve the respective solutions it has already been proposed that the gas supply chamber in the accumulator housing itself be enlarged and that additional supply cylinders connected to the accumulator housing be dispensed with. However, enlargement of the gas supply chamber in the accumulator housing also increases free travel for the separating element or separating membrane, so that it is subjected to heavy wear, such as by folding and overstretching processes, so that failure of the accumulator device soon ensues.

In the case of the solutions discussed in the foregoing with the accumulator cylinder of operating gas mounted on the device, while it has been possible to reduce the clear path of displacement inside the accumulator housing for the separating element, on the whole the operating capacity of the accumulator has been adversely effected, especially with respect to pulsation damping.

In addition, the disclosed solutions have separating elements of an elastomer material which are essentially gas-permeable to a certain extent, so that loss of gas due to diffusion and permeation processes occurs in the long term, the gas supply being transferred to the fluid side.

On the basis of this state of the art the object of the invention is further improvement in the disclosed hydraulic accumulator solutions so that the operating capacity of the accumulator is improved, the accumulator, in an optimized embodiment, requires only little installation space, and gas losses are reduced to the greatest extent. This object is attained with a hydraulic accumulator having the characteristics specified in patent claim 1 or claim 2, each in its entirety.

In that, as specified in the characterizing part of claim 1, there is mounted inside the accumulator housing a mounting device which is positioned inside the gas chamber or delimits it and which provides the possibility of installing the separating element, and in that, in addition, the dimensions of the gas supply chamber are large enough that the entire gas volume required is provided in the accumulator housing itself, additional accumulator cylinders of operating gas on the accumulator housing may be dispensed with. In addition to reduced installation space this configuration provides the advantage of absence of leakage points with the accompanying loss of gas. Since a mounting device is provided for the separating element, less severe operating conditions are possible and incidents of failure of the separating element are prevented to the greatest extent possible.

In another embodiment of the hydraulic accumulator of the same type having the characteristics specified in claim 2 the membrane consists of an elastomer material, a rubber material in particular, which has polytetrafluoroethylene (Teflon®) or its compounds as gas barrier layer. In comparison to the disclosed solutions gas diffusion and permeation processes in the direction of the fluid side are significantly reduced by a separating membrane used for the purpose, one provided with a gas barrier layer; this contributes toward preservation of the operating capacity of the accumulator. Since less gas is lost, less gas also is required for an optimized operating capacity of the accumulator, so that, the performance remaining equal, an accumulator of smaller geometric dimensions may be built.

Other advantageous configurations of the hydraulic accumulator claimed for the invention are specified in the dependent claims.

The hydraulic accumulator claimed for the invention is described in detail in what follows with reference to the drawing, in which the single FIGURE, in the form of a diagram not drawn to scale, shows a longitudinal section through the hydraulic accumulator claimed for the invention.

The hydraulic accumulator is in the form of a so-called membrane accumulator, which is designed to be more or less symmetrical in rotation in relation to its longitudinal axis 10. The accumulator serves the purpose in particular of damping pulsations in fluid circuits, the fluid circuit, in particular one in the form of a hydraulic circuit, not being shown here. The hydraulic accumulator has an accumulator housing identified as a whole here by 12; it is provided on its lower side with at least one inlet 14 and an outlet 16. A separating element 18 in the form of a separating membrane is mounted inside the hydraulic accumulator. The separating element 18 in question separates a gas supply chamber 20 from a fluid chamber 22. In the FIGURE the separating element 18 is shown in its initial state, in which the fluid chamber 22 has been more or less emptied by way of the outlet 16 and the operating gas occupies more or less the entire volume of the gas supply chamber 20.

Depending on the particular operating position of the separating element 18, in which position this element is moving upward as viewed in the direction of the FIGURE, the fluid chamber 22 is correspondingly enlarged and simultaneously the gas volume in the gas supply chamber 20 is reduced. A mounting device 24 is mounted in the accumulator housing 12; this device extends inside the gas supply chamber 20 or delimits this chamber as long as the upper side of the separating element 18, in its fully raised position, is in contact with the lower side of the mounting device 24. As is also to be seen in the FIGURE, the dimensions of the gas supply chamber 20 are large enough so that the entire gas volume required is supplied in the accumulator housing 12 itself without an additional mountable accumulator cylinder.

The separating element 18 as a membrane is in the form of an elastomer material, such as rubber material, and polytetrafluoroethylene or compounds of this substance are used as a gas barrier layer. The substance polytetrafluoroethylene is generally known by the trade name ATeflon,@ which was originally produced by the DuPont manufacturing company. Provision preferably is made such that at least one side, the upper side of the membrane, for example, is coated with polytetrafluoroethylene. In addition or as an alternative, provision may be made such that sealing blocks, that is, agglomerates of polytetrafluoroethylene components, are introduced into the rubber membrane itself. If a gas molecule then encounters such a sealing block inside the membrane, it is directed back toward the gas side and diffusion is still possible only in the intervals between the sealing blocks, this correspondingly reducing the possibility of permeation. In the respective configuration it continues to be ensured that the membrane is highly flexible.

As the FIGURE also shows, the separating element 18, as viewed in cross-section and in the initial state, is designed with a level central bottom area 26 which, in the direction of the annular point of fastening 28 to the mounting surface 24, has a membrane surface 30 which is inclined at an assignable angle to the accumulator housing 12, for example an angle ranging from 20° to 30°, preferably 25°. Reliable uncoiling of the separating element 18 inside the accumulator housing 12 is obtained as a result of the respective configuration, with no need for fear of tearing or the like. In particular, the mounting device 24 has, at least on the mounting side 32 a shape which, figuratively folded through 180° around the transverse axis 34 of the accumulator housing 12, corresponds to the shape of the separating element 18 when the latter is in its initial state.

The separating element 18 is provided in its center with a closing plate 36 which can close off the inlet 14 and the outlet 16 with the separating element 18 in the initial state as shown in the FIGURE. The closing plate 36 is rigidly connected to the separating element 18 by way of a bolted connection 38, a through opening 40 coaxial with the longitudinal axis 10 of accumulator housing 12 being present in the mounting device 24 for engagement of a part of the bolted connection 38 in question, in particular one in the form of the upper part of the screw bolt together with cap nut. It is also ensured by way of the opening 40 in question in the form of an internal hexagon that the parts of the gas supply chamber 20 above the mounting device 24 communicate with the parts of the gas supply chamber 20 which extend between the upper side of the separating element 18 and the lower side of the mounting device 24 in the form of the mounting side 32.

The two housing halves 42, 44 of the accumulator housing 12 are provided on their external circumference side with fastening flanges 46 through which diametrically opposite screw bolts 48 extend to permit assembly of the accumulator housing 12. The inlet 14 and the outlet 16 are mounted in parallel with the longitudinal axis 10 of the accumulator housing 12 so as to discharge into the fluid chamber 22 by way of a common antechamber 50. An optimized flow of the fluid medium into and out of the fluid chamber 22 is thereby obtained, a contribution to this result also being made by the circumstance that the antechamber in question 50 tapers in the direction of the closing plate 36.

The mounting device 24 may be bolted from its external circumference side into the interior of the accumulator housing 12 by way of a screw thread 52, the separating element 18 being additionally secured in the accumulator housing 12 along its fastening edge 28 on the external circumference side by way of a shoulder-like widening 54 on the lower side of the mounting device 24. The mounting surface of the widening 54 on the external circumference side is at least in part in contact with the edge-like widening of the fastening point 28 of the separating element 18.

As the FIGURE also shows, the upper housing half 42 is configured in cross-section as a cavity elliptical or hemispherical in cross-section, while the lower housing half 44 on the fluid side 22 is configured as a level plate 56 at least in the area on the inlet and outlet sides. The upper housing half 42 has in its center a connecting point 58 which is closed by a screw plug 60, which is removed to permit refilling of the accumulator. The processes involved are known, so that they will not be described in detail here. The operating capability of the accumulator is correspondingly increased by choice of the cavity referred to on the gas supply side without the need for use of additional assemblies such as additional cylinders or the like.

The hydraulic accumulator claimed for the invention possesses high operating capability, requires little installation space, and has a long service life, since the separating element 18 may be provided with a gas barrier layer and, in addition, the uncoiling of the separating element 18 is controlled as desired and overstretching of the separating membrane is reliably prevented by way of the appropriately configured mounting side 32 of the mounting device 24. 

1. A hydraulic accumulator, in particular a membrane accumulator, in particular for damping pulsations in fluid circuits, having an accumulator housing (12) with at least one inlet (14) and an outlet (16) for the fluid to be damped, a separating element (18), preferably in the form of a membrane, separating a gas supply chamber (20) from a fluid chamber (22) inside the accumulator housing (12), characterized in that there is mounted inside the accumulator housing (12) a mounting device (24) which extends inside the gas supply chamber (20) or delimits such chamber and which provides the possibility of mounting the separating element (18), and in that the dimensions selected for the gas supply chamber (20) of the accumulator housing (12) are large enough so that the entire volume of gas required is stored in the accumulator housing (12) itself.
 2. A hydraulic accumulator, in particular a membrane accumulator, in particular for damping pulsations in fluid circuits, having an accumulator housing (12) with at least one inlet (14) and an outlet (16) for the fluid to be damped, a separating element (18), preferably in the form of a membrane, separating a gas supply chamber (20) from a fluid chamber (22) inside the accumulator housing (12), characterized in that the membrane consists of an elastomer material, in particular of a rubber material, and has as gas barrier layer polytetrafluoroethylene or compounds of this substance.
 3. The hydraulic accumulator as claimed in claim 2, wherein the membrane is coated on at least one side with polytetrafluoroethylene and/or is introduced into the membrane in the form of sealing blocks.
 4. The hydraulic accumulator as claimed in claim 1, wherein the separating element (18) as viewed in the initial state has a level bottom area (26) which has in the direction of the annular point (28) of fastening to the accumulator housing (12) a membrane surface (30) inclined at an assignable angle to the mounting device (24).
 5. The hydraulic accumulator as claimed in claim 1, wherein the mounting device (24) has, at least on its mounting side, a shape which, figuratively folded through 180° around a transverse axis (34), corresponds to the shape of the separating element (18) in its initial state.
 6. The hydraulic accumulator as claimed in claim 1, wherein the separating element (18) is provided at its center with a closing plate (36) for the inlet and the outlet (14, 16), such closing plate being rigidly connected to the separating element (18) by way of a bolted connection (38) and wherein there is present in the mounting device (24) a through opening (40) for engagement of a part of such bolted connection (38).
 7. The hydraulic accumulator as claimed in claim 1, wherein the two housing halves (42, 44) of the accumulator housing (12) are provided on their external circumference side with fastening flanges (46) through which diametrically opposite screw bolts (48) extend and which permit assembly of the accumulator housing (12).
 8. The hydraulic accumulator as claimed in claim 1, wherein the inlet (14) and the outlet (16) discharge into the fluid chamber (22) in parallel with the longitudinal axis (10) of the accumulator housing (12) by way of a common antechamber (50).
 9. The hydraulic accumulator as claimed in claim 1, wherein the mounting device (24) may be screwed into the interior of the accumulator housing (12) by its external circumference side and wherein the separating element (18) is additionally retained in the accumulator housing (12) along its fastening edge (28) on the external circumference side by way of a shoulder-like widening (54).
 10. The hydraulic accumulator as claimed in claim 1, wherein the part (42) of the accumulator housing (12) which delimits the gas supply chamber (20) is configured as a cavity elliptical or hemispherical in cross-section and wherein on the fluid side (22) the accumulator housing (12) is configured on the inlet and outlet sides (14, 16) as a more or less level plate (56). 